That particular recipe is, as the author notes, austere--so if that sounds good to you, I would leave it as is. What I mean is, if you were starting with a heartier beef pho I might suggest changing more, but that recipe is pretty flexible I would think. You could, now that I think about it, get sushi quality shellfish and place it raw in the bowl before ladling the broth over it, much as the Vietnamese would do with thin slices of raw sirloin in beef pho. But I only recommend that if you have stellar shrimp (or scallops would work nicely too, thinly sliced).

First of all ,we had this the other night, I used leftover chicken, it was great. However, your guest is pescatarian right? I would go shrimp, fish or veggie. If you go veggie you may want to amp up the spices.